1. Field of the Invention
The invention relates generally to a fire protection sprinkler system, and more particularly to fire protection sprinkler systems for attics.
2. Description of the Related Art
Pitched overhead walls in buildings hold special challenges for fire sprinkler systems, particularly where beams, trusses or joists project from or are otherwise exposed beneath the lower side of the overhead wall, which may be an interior cathedral-type ceiling, the lower deck of a pitched roof, or the attic space of the underside of a pitched roof.
NFPA 13, the National Fire Protection Association standard for the installation of sprinkler systems, applies to the installation of sprinklers beneath pitched overhead walls.
Sprinklers are mounted beneath a pitched overhead wall on supply manifolds which may run perpendicular or parallel to the peak. Based on the fire hazard (light, ordinary, or extraordinary), NFPA 13 specifies adequate spacing between the supply lines and between individual sprinklers on the lines and maximum protection area per sprinkler. Under light hazard conditions, adjoining sprinklers and supply lines may be as far as fifteen feet apart, with each sprinkler allocated a floor space of up to 225 square feet to protect. For ordinary or extraordinary hazards, the protection area per sprinkler is reduced to between about 100 and 130 square feet with appropriate reductions in the spacings between individual sprinklers and supply lines to provide such average coverage.
NFPA 13 also specifies the orientation of a sprinkler's deflector with respect to overhead walls. Where conventional automatic ceiling sprinklers are employed, the sprinklers are mounted with their deflectors oriented parallel to the overhead wall beneath which they are installed. Unless otherwise listed, a residential upright sprinkler deflector should be positioned 1 to 4 inches below the overhead wall, and a residential sidewall sprinkler deflector should be positioned 4 to 6 inches below the overhead wall.
In cases where a sprinkler is installed directly beneath the peak of a pitched roof, its deflector may be oriented horizontally. Also, per NFPA 13 (8.6.4.1.3), the deflectors of sprinklers that are located below and near the peak, rather than directly under the peak, are to be no more than 36 inches below the peak, except on a steeply pitched roof, where the distance may be increased to assure a horizontal clearance of not less than two feet from other structural members on either side of the sprinkler. Apart from these restrictions, sprinklers are permitted to be installed otherwise in accordance with their listings with respect to their spacing from one another and along branch lines and with respect to the spacing of their deflectors from the overhead wall.
Conventional fire sprinkler protection practice, as embodied in NFPA 13, is directed to controlling fires occurring beneath the sprinklers and not to controlling fires which may occur above the sprinklers.
Prior attempts to provide a residential attic sprinkler system in compliance with NFPA 13 have been made, notably in U.S. Pat. No. 5,669,449. In that patent, the inventors catalog failed attempts to comply with the NFPA 13 specification for this application using conventional sidewall sprinklers.
In particular the inventors of the '449 patent found in actual fire tests that the installation of conventional, modern ceiling sprinklers in pitched roofs in accordance with NFPA 13 can permit secondary fires to start and burn above the sprinklers, particularly in areas in the peak of the roof or a cathedral ceiling, which is not adequately protected by conventional sprinklers installed in accordance with NFPA 13 requirements. Those inventors found this to be particularly true where structural members such as beams, joists, trusses or the like project downwardly from the deck of the pitched overhead wall to form courses. With such a structure, the courses between adjacent beams direct heated air from a fire straight up the pitched portion of the ceiling or roof to the peak. The deflectors of standard ceiling sprinklers are configured to direct the water released by the sprinkler essentially downward in a fairly restricted cone. The '449 inventors concluded that it is often difficult or impossible even to locate and position such sprinklers in a way which conforms with NFPA 13 and yet so that their discharge is directed into one of the channels to cover the channel fully and cool any heated air which may be rising through the channel.
The '449 inventors attempted to overcome the prior problem by installing standard sidewall sprinklers at the peak of a pitched test roof. Sidewall sprinklers differ from ceiling sprinklers primarily in their deflectors and in the resulting spray distribution patterns. The spray distribution patterns of ceiling sprinklers are generally symmetric and conical with respect to a centerline of the sprinkler, entirely around the sprinkler. Sidewall sprinklers discharge primarily outwardly from one side or end of the sprinkler. Conventional sidewall sprinklers provide a water distribution in which the outward (longitudinal) throw of water is greater than the lateral spread of the water, resulting in an “elliptical” or “rectangular” distribution pattern.
When the inventors of the '449 patent experimented with pairs of conventional sidewall sprinklers installed in the peak of a pitched test roof, with each sprinkler directed to throw its water down a separate one of the two courses which come together at the peak, it was found impossible to locate such sidewall sprinklers in a way in which the spray from one would not cover the other, cooling the other sprinkler and preventing its activation (known as a “cold solder” condition). Furthermore, in a significant number of instances, it was the sidewall sprinkler directed down the wrong course that would activate first, and prevent the proper fire suppressing sidewall sprinkler from ever activating.
It is believed that there is a distinct and significant need for better fire protection for pitched overhead walls such as cathedral-type ceilings and the lower sides of pitched roofs capable of utilizing suitable upright sprinklers as well as suitable sidewall fire protection sprinklers.